The invention relates to a gas generator, and specifically a gasifier which gasifies combustible or carbonizable solid materials, and more particularly to a gravity type gasifier wherein the combustible materials to be gasified move through a loading zone at the top of the gasifier, and pass successively through a drying zone, a pyrolyzing zone, a cracking zone where the tars are cracked, a reduction zone where the gas is generated and an oxidation zone. The starting materials include waste wood and biomass, for example. Both charcoal and combustible gas are obtained in this process. With such gasifiers, there are the objectives of reducing the need for energy to heat the combustible material in the drying chamber, of maximizing cracking of the tars for reducing the quantity of tars released in the processing, and of improving the inflow of oxidizing air. There are numerous gasifiers and various techniques are known for achieving the foregoing goals. An example of such a gasifier is shown in U.S. Pat. No. 4,344,772.
In conventional downflow, gravity type gasifiers, there is a natural limitation in the internal cross-section of the reaction chamber. Once that natural limitation in cross-section is exceeded, the cracking process becomes uncontrollable and excessive tar is generated. The invention is designed to reduce the generated tars.
There is an external cooling jacket especially located at the lower part of the gasifier. Steam is generated there in abundant quantities. A large part of the steam is utilized in the combustible gas generation process. One of the objectives of the invention is to make use of that steam to heat the combustible material drying chamber located toward the top of the apparatus.
Finally, the oxidation air is typically introduced about the periphery of the thermo-chemical reactor. One of the objectives of the invention is to improve the delivery of air and make a more uniform oxidation zone so that the combustible material being degasified is more uniformly treated and the process is improved.